This invention relates to a mechanical amplification mechanism for a piezoelectric element, and more particularly to a lever arm structure thereof.
In the U.S. Pat. No. 4,675,568 issued on Jan. 23, 1987 , there is proposed a mechanical amplification mechanism for electromechanical transducer to be used for dot impact printers.
In the prior art as shown in FIG. 1A and FIG. 1B, a pair of lever arms 50 are respectively connected to both end faces of a piezoelectric element 10 and of a base block 40 through bottle necked holding portions 20 and fulcrum portions 30. The lever arms 50 hold a beam 60 in a sandwiching fashion at their opposite ends of the holding portions 20. The beam 60 had a printing needle 601 which is an acting element. The base block 40 is provided with a pair of attachment holes 41 and an adjustment screw 602 to be used for a backstop of the beam 60.
The mechanical amplification mechanism is required to maximize the energy conversion efficiency at the position of the printing needle 601. Therefore, the lever arms 50, the holding portions 20, the fulcrum portions 30 and the base block 40 have been made of the same and highly rigid materials such as stainless steel and structured integrally so as to transmit the force generated by the piezoelectric element to the beam 60. In order to effectively transmit the displacement or generated force of the piezoelectric element 1, it is integrally made of highly rigit materials of a large plate thickness T. It is respectively formed to have the fulcrum portions 30 and the holding portions 20 having the width W smaller than the plate thickness T to have small flexural modules.
The plate thickness T which can be punched out by a press is usually limited to a dimension equivalent to the width of the fulcrum portions 30 and the holding portions 20 (T .ltoreq. W). As the conventional mechanical amplification mechanism needs the plate thickness T which is larger than the width W, it is impossible to use the punching process although the method is optimal for mass-producing the mechanism with a high dimensional precision. The manufacturing method is therefore quite limited for lever arms 50. For instance, if a write-cut electric spark method is used for manufacture, it requires longer time and higher costs even though it is most suitable for small quantity productions. The lost wax casting process or powder metallurgy may be used for manufacture, but they impose restrictions in respect of dimensions and shapes. If these methods are used, voids are often generated at the time when the bottle necked portions 20 and 30 are being molded, thus deteriorating mechanical strength and dimensional precisions. The conventional mechanism thus has limitations for the manufacture and causes problems in price, dimensional precision and mechanical strength.
Moreover, as the bottle necked portions 20 and 30 are integrally formed of the same material, if a trivial flaw is caused in processing, stress becomes concentrated on the point to subsequently accelerate metalic fatigue and to shorten dynamic durability.